In situ and remote sensing of turbulence in support of the aviation community Larry B. Cornman National Center for Atmospheric Research USA
The Motivation Turbulence is the main cause of in-flight injuries for both passengers and flight attendants. After a severe encounter, the airline has to perform a structural check on the aircraft. Pilots will try to re-route around an area if there have been reports of moderate or greater turbulence. Tstorm & windshear Icing Precip Ceil & Vis Part 121 Other Turbulence Bottom-line: Turbulence is a safety problem as well as having a large financial impact on the airlines. Weather-related accidents for large transport aircraft
DC-8 Cargo Aircraft Damaged Due to Extreme Turbulence Missing Something?
The Turbulence Problem for Aviation (Grossly Oversimplified) Turbulent eddies larger than 100 meters and smaller than 3000 meters (approximately) produce aircraft motions which can be difficult -- or impossible -- to control. With small-amplitude eddies, these induced motions may be simply uncomfortable to passengers. Large amplitude eddies, on the other hand, can result in passenger injuries or even structural damage to the aircraft.
Turbulence Scales of Motion Large eddies Turbulent eddies Small eddies 10 s km Aircraft responds to scales from approx. 100 m 3 km cm NWP resolution Mesoscale model resolution Fine-scale model resolution
The product of the response function and the wind spectrum gives the output spectrum. Response Function for Transport Aircraft 2000 m 100 m Von Karman Spectra
The Need For Turbulence Measurements Tactical: Real time alerts of eminent encounter (< 1 min.) Turn seat belt sign on. Get passengers seated and in seatbelts. Get service carts stowed and flight attendants seated. Real time alerts/nowcast of impending encounter (< 15 min.) All of the above. Change altitude. Change flight path.
The Need For Turbulence Measurements Strategic: Nowcast/Forecast of potential encounter (en route) Increase pilot awareness. Discussions with airline Dispatch personnel. Discussions with en route air traffic personnel. Consider altitude/course change. Forecast of potential encounter (pre-flight) Pre-flight awareness for pilot/dispatch. Consider re-routing flight path.
In situ Turbulence Measurement and Reporting System Goal: To augment/replace subjective PIREPs with objective and precise turbulence measurements. Features: Atmospheric turbulence metric: eddy dissipation rate (EDR). EDR can be scaled into aircraft turbulence response metric (RMS-g). Adopted as ICAO Standard
Increase in Spatial/temporal Coverage: UAL EDR Reports Compared to pireps 1.3 million EDR reports/month from 100 or so aircraft - compared to 55k pireps from all aircraft. 737 757 737 + 757
In situ measurement and reporting system Implemented on ~ 200 UAL aircraft since 2000 Implementation status SWA: Fleet implementation on ~ 280 737-700s in CY08 DAL: Fleet implementation on ~ 120 737-800s in CY08 NWA: Discussions ongoing for implementation on ~ 140 Airbus 319/320s and 56 787s UAL: 757 ACMS replacement AAL: Discussions ongoing Website: UAL 757 edr flight tracks overlaid on GTG forecasting product
NASA Airborne Radar Detection of Turbulence Program RMS winds RMS g-load From NASA B-757 Aircraft 19:12:02 19:13:44
Event 232-10 (19:12:02, 19:12:13, 19:12:25) -1:42-1:31-1:19 Hazard detected 1:19, 18 km to encounter
Event 232-10 (reflectivities at 19:12:25) -1:19
Event 232-10 (19:12:37, 19:12:49, 19:13:01) -1:07-0:55 Persistent detection -0:43
Flight Track for NASA flight R232 Event R232-10 North-Central Alabama
NEXRAD in-cloud turbulence detection algorithm (NTDA) Cockpit display or radioed alert Graphic courtesy of virtualskies.arc.nasa.gov Dispatch, ATC, etc. NEXRAD or TDWR In-cloud edr display
Case Study: Severe turbulence encounter at FL 310 over NE Arkansas Vertical acceleration from -0.9 g to +2.3 g in about 3 seconds 43 minor injuries, two serious; cabin damage 8 min. warning could have reduced/eliminated injuries X X
NTDA uplink demonstration Uses data from 83 NEXRADs, covering eastern US 3-D EDR mosaic updated every 5 minutes, displayed via Experimental ADDS ACARS text uplinks to UAL cockpits for flights registered on NCAR webpage Pilot feedback via webpage September press release garnered significant attention /EXPERIMENTAL TURBULENCE FI UAL /AN N UA UPLINK -- 05 Sep 2006 21:38:13Z FL 300 orient. 83 deg '+'=waypoint, '*'=route, 'X'=aircraft at 38.3N, 80.6W ' '=no_data, 'o'=smooth, 'l'=light, 'M'=mod, 'S'=severe -----------------------(52 to IAD)------------------------ * * MM * MM * MM l lll M * MMM lollo * lml oolo * l oo * * 080 * M llllllll ll * MM lllllllllllllll l * lll lllllllllollllllll * MMl l MMllllllllooollllll * MMl l MMMl lllllllllollll * MM l MMMM llll llol ll * MM MMMM ll * MMS MMM * MSS MM * MSS +PUTTZ + MSS * SSSSSS MSS M l S*SSSSSSSSS MSS M llls*sssmsssss MSS l lsms*smmmmssss MSS l SSMM*MMMMMMMM MSS M MM*SMMMMMMMMlllll MSS M M*SSMMMMMMMMllllll MMM M *MMMMMMMMMMMMMllll MMM * MMlllMMMlMllllllM lll 040 * lllllllllllllllllmml lll * llllllllllllll lls * llllllllll MMS * lllllll SSS * lllll SSS * lll MMS * l ll MM * MM M MM*MM o MSS SM*MM MMM MM *MM l MM MMMSS S * l l lm MMMSSM * lllllll o l l MMMM * lllllo MMMMM * llllll M * lllll SSS * llll ll SSS M l * l lll SSS Mlllll * llm MM lmlllll * l ------- ---------valid- --------X-------- ---------------- -90 +90 Left 40 2135Z (18 from 3819N/8058W) Right 40 Flight information Legend Route Waypoint Severe turbulence Moderate turbulence Aircraft position Vertical cross-section
Diagnosis of convectively-induced turbulence (DCIT) Near-storm environment and turbulence diagnostics from RUC Storm location, morphology, and observations from satellite, radar (dbz and EDR), and lightning Associations with in situ EDR reports used to tune an empirical model (random forest) DCIT provides tactical 3-D gridded EDR, Prob MoG and Prob SoG assessments for use in GTGN DCIT real-time prototype running in RAL since August DCIT: Prob MoG (uncalibrated) 27 June 2007 2300 UTC, FL 300 RUC only RUC+obs
Turbulence Detection via Airborne GPS Receivers: The Concept Airborne receivers would be a platform of opportunity to collect occultations in the cruise regime of commercial aviation, e.g., 20-40 kft. AGL. The turbulence measurements from these occultations would probably not be used as stand-alone information, but integrated into operational nowcast/forecast products.
Geometry of the Problem η 1 R η 1 1 is the distance, along the LOS, from the satellite to the center of the turbulence patch. R is the distance from the satellite to the aircraft receiver along LOS. Δη is the width of the turbulence patch along LOS. R η 1 is the distance from the aircraft to the turbulence patch. Δη R η
Aircraft Flight Track with GPS Occultations
Parameter Estimation 1000 realizations Maximum Likelihood (ML) estimation of intensity with fixed R η1 = 100 km while varying L0. Horizontal and vertical lines are simulated (i.e., true ) values.
Parameter Estimation (cont d) 1000 realizations ML estimation of intensity with fixed while varying. R η 1 L 0 = 3 km
Initial ML estimation of intensity (left) and using an estimate of (right). η 1 Solid vertical line is true value. Blue values are from using the high-frequency portion of the spectrum, red values use all the spectral points. R η 1 Simulated value is 100 km, guess is 10 km - i.e., an underestimate hence the overestimate of the intensity.
Detection of Turbulence Using an Airborne Forward-Looking IR Sensor Possible Approach: Derive equation that relates the statistics of the atmospheric turbulence (e.g., temperature field) to those of the sensor measurables. Consider the irradiance (H) at a given frequency, measured at the aircraft (x=0): 0 H (0) = WB ( T ( x)) f ( x) dx L Where W B is the Planck function, L is the path length over which the measurement is made, and f is a combined function of the nonturbulent atmosphere and the response characteristics of the sensor.
Detection of Turbulence Using an Airborne Forward-Looking IR Sensor Next, consider the same measurement when the aircraft has moved a distance ρ : ρ H ( ρ) = WB ( T( x)) f( x) dx L+ ρ Assuming that the Planck function is linear in the temperature, the correlation function of the irradiances can be computed: 0 ρ H (0) H( ρ) K T( x) T( x ) f( x) f( x ) dxdx = LL+ ρ
Detection of Turbulence Using an Airborne Forward-Looking IR Sensor Assuming that standard turbulence theory applies, 2 T( x) T( x ) = CT g( x x) 2, where C T is the intensity parameter of the turbulent temperature field. In principle the turbulence intensity parameter is given by: C 2 T = 0 ρ H(0) H( ρ ) K g( x x) f ( x) f ( x ) dxdx LL+ ρ
Detection of Turbulence Using an Airborne Forward-Looking IR Sensor Issues: Aircraft respond to vertical wind motions, not temperature fluctuations - the relationship between the two is not well-understood. To what spatial scales are these IR devices sensitive?
Turbulence Forecast Product: Graphical Turbulence Guidance (GTG) Based on RUC NWP forecasts Uses a combination of turbulence diagnostics, merged and weighted according to current performance (pireps, EDR) Current work areas: Probabilistic forecasts of moderate-or-greater (MOG) turbulence Optimal use of in situ reports Output probability of MOG,SOG > some EDR threshold Improve forecasts of severe turbulence
Ellrod1 DTF3 UBF Ri -NVA NCSU1 GTG = Weighted ensemble of turbulence diagnostics FRNTGth CLIMO NCSU2 GTG VWS TEMPG EDRS10 0 h forecast valid at 22 Sep 2006 15Z
GTG improvement using in situ data over pireps Null MOG w/ Pireps w/ In Situ ROC Curve Intensity Discrimination
Turbulence Nowcasting System (GTG-N) Overview Motivation: GTG updates are tied to the model runs (once per hour). Turbulence can vary dramatically over small space/time intervals. We will have more observational data and rapidupdate diagnostic products in the near future. This implies the need for a rapid-update (e.g., every 15 min) gridded turbulence product, GTG-N
GTG-N Overview Approach (nominal): Start with GTG grid. Incorporate: DCIT/NTDA In situ Reports Pireps Lightning data Satellite data. Other Compute confidences for all inputs (diagnostic and measurements). Use an intelligent merging procedure to create a unified turbulence nowcast gridded product.
Turbulence Nowcasting System: GTG-N Merges all current turbulence observations with forecast grids. Cockpit display or alert (EDR or RMS-g) Graphic courtesy of virtualskies.arc.nasa.gov Dispatch, ATC, etc. In situ EDR reports, PIREPs, 4D data cube updated every ~15 min GTG forecast grids (EDR) Convective turbulence diagnostic (EDR) Radar (NTDA) turbulence grids (EDR) Wx satellite data
GTG-N Example GTG 1 hr forecast blend DCIT pireps In situ tracks
Summary Turbulence measurements are critical in providing accurate and operationally useful tactical and strategic information to users. In situ turbulence measurements are now available and used operationally more to come. A number of proof-of-concept sensor demonstrations have occurred, with positive results. Other technologies in development/evaluation: Airborne lidar Satellite GPS/Iridium Airborne IR